. The anatomy of the domestic animals. Veterinary anatomy. 84 THE SKELETON OF THE HORSE overhung by the ventral turbinate bone; it is much the largest and is the direct path between the nostrils and posterior nares. The osseous nasal aperture (Apertura nasi ossea) is bounded by the nasal bones and the premaxillse. The posterior extremity or fundus is separ- ated from the cranial cavity by the cribriform plate of the ethmoid, and is largely occupied by the lateral masses of that bone. THE PARANASAL SINUSES Connectetl directly or indirectly with the nasal cavity, of which they are diverticula, a
. The anatomy of the domestic animals. Veterinary anatomy. 84 THE SKELETON OF THE HORSE overhung by the ventral turbinate bone; it is much the largest and is the direct path between the nostrils and posterior nares. The osseous nasal aperture (Apertura nasi ossea) is bounded by the nasal bones and the premaxillse. The posterior extremity or fundus is separ- ated from the cranial cavity by the cribriform plate of the ethmoid, and is largely occupied by the lateral masses of that bone. THE PARANASAL SINUSES Connectetl directly or indirectly with the nasal cavity, of which they are diverticula, are four pairs of air-sinuses (Sinus paranasales), viz., maxillary, frontal, sphenopalatine, and ethmoidal. The maxillary sinus (Sinus maxillaris) is the largest. Its lateral wall is formed l)y the maxilla, the lacrimal, and the malar. It is Ijounded medi- ally- fiy the maxilla, the ventral turbinate, and the lateral mass of the ethmoid bone. It extends backward to a transverse plane in front of the root of the supraorbital process, and its anterior limit is indicated approximately by a line drawn from the anterior end of the facial crest to the infraorljital foramen. Its dorsal boundary cor- responds to a line drawn backward from the in- fraorbital foramen parallel to the facial crest. The ventral wall or floor is formed by the alve- olar part of the maxilla; it is very irregular and is crossed by bony plates running in various directions. The last three cheek teeth project up into the cavity to an extent which varies with age; they are covered by a thin plate of bone. The cavity is divided into anterior and posterior parts by an oblique septum (Septum sinus maxillaris). The lateral margin of the sep- tum is commonly about two inches (ca. 5 cm.) from the anterior end of the facial crest; from here it is directed inward, backward, and up- ward. The upper part of the septum (formed by the posterior end of the ventral turbinate bone) is very delicate and usually Fig.
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